Zoom lens and image-pickup apparatus having the same

ABSTRACT

At least one exemplary embodiment is directed to a zoom lens which includes first to fourth lens groups, each moving and having negative, positive, negative, and positive refractive power, arranged from an object to an image in that order. The second lens group includes a second A lens component composed of a single positive lens, and a second B lens component composed of a negative lens and a positive lens with positive refractive power as a whole, arranged from the object to the image in that order. The second A lens component displaces images in a direction substantially perpendicular to an optical axis by having a component of it&#39;s displacement perpendicular to the optical axis, and the zoom lens satisfies the following condition: 0.2&lt;f2/f2A&lt;0.6, where f2A and f2 are focal lengths of the second A lens component and the second lens group, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to zoom lenses, more particularly thoughnot exclusively, to zoom lenses used in image-pickup apparatuses.

2. Description of the Related Art

Recently, image-pickup apparatuses, such as a photographic camera, avideo camera, and a digital camera, have been demanded to have higherquality images.

Furthermore, because of the expansion in shooting conditions, it wouldbe useful for the lenses used in these apparatuses to be zoom lenseshaving image stabilizing performances for correcting blurring due tocamera shake.

A method of compensating vibration includes decentering selected lensgroups arranged in parallel with a direction substantially perpendicularto an optical axis. This method needs no additional optical system forcompensating vibration.

This method also has merits that the lens groups for vibrationcompensating can be mostly simplified and an actuator for vibrationcompensating can be miniaturized by suppressing a drive torque.

On the other hand, there is a so-called negative lead type zoom lens inthat a lens group with negative refractive power is preceding (locatedat a position closest to an object). In this zoom lens, a distance ofcontact shooting is comparatively small, a shooting field angle can beincreased rather easily, and a back focus can be increased comparativelyeasily so as to be frequently used in a wide-field angle taking lens.

A two-group zoom lens composed of first and second lens groups withnegative and positive refractive power arranged from the object in thatorder, has been known as the negative lead type zoom lens having imagestabilizing performances (Japanese Patent Laid-Open No. 10-161024 andNo. 7-64025). In this two-lens group, the vibration is compensated bymoving part of the second lens group in a direction substantiallyperpendicular to the optical axis.

Also, a four-group zoom lens, composed of first to fourth lens groupswith negative, positive, negative, and positive refractive powerarranged from the object in that order, has been known, in which thevibration is compensated by moving part of the second lens group in adirection substantially perpendicular to the optical axis (JapanesePatent Laid-Open No. 9-113808 and No. 2004-61910).

In the two-group zoom lens discussed in Japanese Patent Laid-Open No.10-161024 and No. 7-64025, the variable power is given only to thesecond lens group. Hence, when the lens is zoomed at a high ratio, thevariations in aberration due to the zooming are difficult to besuppressed.

Since the displacement of the second lens group during zooming iscomparatively large relative to the zoom ratio, the entire lens systemis difficult to be miniaturized.

The vibration is compensated by parallel decentering part of the secondlens group; however, when the lens is zoomed at a high ratio, theincreasing tendency of aberration due to the vibration compensating hasbeen shown.

In the four-group zoom lens discussed in Japanese Patent Laid-Open No.9-113808 and No. 2004-61910, the vibration is compensated by moving aplurality of lenses in a direction substantially perpendicular to theoptical axis, so that the weight of the moving part is increased and thelens frame therefore is also increased in size. Thus, a large load isapplied to a drive system for correcting the blurring (compensating thevibration), resulting in an increasing tendency in size of the camerashake drive system.

When the vibration is compensated by decentering the lens, there can bea delayed response in decentering the lens.

In the zoom lens having a image stabilizing mechanism for use in a highquality image-pickup apparatus, it would be useful that the lens forcorrecting the image blur is small in size and weight and thedeterioration in optical performances is small during compensating thevibration.

SUMMARY OF THE INVENTION

At least one exemplary embodiment is directed to zoom lenses used inimage-pickup apparatus (e.g., a digital still camera, a video camera,and a surveillance camera) using solid state image devices.

An exemplary embodiment of the present invention is directed to a zoomlens where the load of a driving device, configured to compensate forvibration (image stabilizer), is small, and the entire apparatus can beminiaturized. Additionally an exemplary embodiment efficientlycompensates for the vibration and can include an image-pickup apparatushaving the zoom lens.

A zoom lens according to at least one exemplary embodiment of thepresent invention includes a first lens group with negative refractivepower, a second lens group with positive refractive power, a third lensgroup with negative refractive power, and a fourth lens group withpositive refractive power, which are arranged from an object side to animage side in that order. Each of the lens groups moves so that thespace between the first lens group and the second lens group is reduced,the space between the second lens group and the third lens group isincreased, and the space between the third lens group and the fourthlens group is reduced, at a telephoto end in comparison with spacing ata wide angle end. The second lens group includes a second A lenscomponent composed of a single positive lens, and a second B lenscomponent composed of a negative lens and a positive lens with positiverefractive power as a whole, which are arranged from the object side tothe image side in that order. The second A lens component displacesimages in a direction substantially perpendicular to an optical axis byhaving a component of it's displacement perpendicular to the opticalaxis, and in which the zoom lens satisfies the following condition:0.2<f2/f2A<0.6,where f2A and f2 are focal lengths of the second A lens component andthe second lens group, respectively.

A zoom lens according to at least one exemplary embodiment of thepresent invention includes a first lens group with negative refractivepower; a second lens group with positive refractive power; an aperturestop; and trailing lens groups, which are arranged from an object sideto an image side in that order. The space between the first lens groupand the second lens group is changed during zooming, and the second lensgroup includes a second A lens component composed of a single positivelens, and a second B lens component composed of a negative lens and apositive lens with positive refractive power as a whole, which arearranged from the object side to the image side in that order. Thesecond A lens component displaces images in a direction substantiallyperpendicular to an optical axis by having a component of it'sdisplacement perpendicular to the optical axis, and in which the zoomlens satisfies the following conditions:0.2<f2/f2A<0.60.4<LP/fw<1.0,where f2A and f2 are the focal lengths of the second A lens componentand the second lens group, respectively; LP is the distance along theoptical axis between the lens surface closest to the image side of thesecond A lens component and the aperture stop; and fw is the focallength of the entire system at the wide angle end.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lens sectional view at a wide angle end of exemplaryembodiment 1 according to the present invention.

FIGS. 2A and 2B are longitudinal aberration drawings at the wide angleend and at a telephoto end, respectively, of exemplary embodiment 1according to the present invention.

FIGS. 3A to 3D are lateral aberration drawings at wide angle andtelephoto ends and for base and image stabilization periods,respectively, of exemplary embodiment 1 according to the presentinvention.

FIG. 4 is a lens sectional view at the wide angle end of exemplaryembodiment 2 according to the present invention.

FIGS. 5A and 5B are longitudinal aberration drawings at the wide angleend and at the telephoto end, respectively, of exemplary embodiment 2according to the present invention.

FIGS. 6A to 6D are lateral aberration drawings at wide angle andtelephoto ends and for base and image stabilization periods,respectively, of exemplary embodiment 2 according to the presentinvention.

FIG. 7 is a lens sectional view at the wide angle end of exemplaryembodiment 3 according to the present invention.

FIGS. 8A and 8B are longitudinal aberration drawings at the wide angleend and at the telephoto end, respectively, of exemplary embodiment 3according to the present invention.

FIGS. 9A to 9D are lateral aberration drawings at wide angle andtelephoto ends and for base and image stabilization periods,respectively, of exemplary embodiment 3 according to the presentinvention.

FIG. 10 is a lens sectional view at the wide angle end of exemplaryembodiment 4 according to the present invention.

FIGS. 11A and 11B are longitudinal aberration drawings at the wide angleend and at the telephoto end, respectively, of exemplary embodiment 4according to the present invention.

FIGS. 12A to 12D are lateral aberration drawings at wide angle andtelephoto ends and for base and image stabilization periods,respectively, of exemplary embodiment 4 according to the presentinvention.

FIG. 13 is a lens sectional view at the wide angle end of exemplaryembodiment 5 according to the present invention.

FIGS. 14A and 14B are longitudinal aberration drawings at the wide angleend and at the telephoto end, respectively, of exemplary embodiment 5according to the present invention.

FIGS. 15A to 15D are lateral aberration drawings at wide angle andtelephoto ends and for base and image stabilization periods,respectively, of exemplary embodiment according to the presentinvention.

FIG. 16 is a schematic view of part of an image-pickup apparatusaccording to an exemplary embodiment the present invention.

DESCRIPTION OF THE EMBODIMENTS

The following description of at least one exemplary embodiment is merelyillustrative in nature and is in no way intended to limit the invention,its application, or uses.

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the relevant art may not be discussed in detail butare intended to be part of the enabling description where appropriate,for example the fabrication of the lens elements and their materials.

In all of the examples illustrated and discussed herein any specificvalues, for example the focal lengths, should be interpreted to beillustrative only and non limiting. Thus, other examples of theexemplary embodiments could have different values.

Notice that similar reference numerals and letters refer to similaritems in the following figures, and thus once an item is defined in onefigure, it may not be discussed for following figures.

Note that herein when referring to correcting or corrections of an error(e.g., an aberration), a reduction of the error and/or a correction ofthe error is intended.

Embodiments of a zoom lens and an image-pickup apparatus having the zoomlens according to the present invention will be described below.

FIG. 1 is a lens sectional view of a zoom lens of an exemplaryembodiment 1 at a wide angle end (short focal length end), and FIGS. 2Aand 2B are longitudinal aberration drawings of the zoom lens of theexemplary embodiment 1 at the wide angle end and at a telephoto end(long focal length end), respectively.

FIGS. 3A and 3B are lateral aberration drawings of the zoom lens of theexemplary embodiment 1 at the wide angle end and at the telephoto end,respectively, for a base period (without image stabilization).

FIGS. 3C and 3D are lateral aberration drawings of the zoom lens of theexemplary embodiment 1 at the wide angle end and at the telephoto end,respectively, for a image stabilization period when a deflectioninclination of 0.3° is corrected.

FIG. 4 is a lens sectional view of a zoom lens of an exemplaryembodiment 2 according to the present invention at the wide angle end,and FIGS. 5A and 5B are longitudinal aberration drawings of the zoomlens of the exemplary embodiment 2 at the wide angle end and at thetelephoto end, respectively.

FIGS. 6A and 6B are lateral aberration drawings of the zoom lens of theexemplary embodiment 2 at the wide angle end and at the telephoto end,respectively, for the base period.

FIGS. 6C and 6D are lateral aberration drawings of the zoom lens of theexemplary embodiment 2 at the wide angle end and at the telephoto end,respectively, for the image stabilization period when a deflectioninclination of 0.3° is corrected.

FIG. 7 is a lens sectional view of a zoom lens of an exemplaryembodiment 3 according to the present invention at the wide angle end,and FIGS. 8A and 8B are longitudinal aberration drawings of the zoomlens of the exemplary embodiment 3 at the wide angle end and at thetelephoto end, respectively.

FIGS. 9A and 9B are lateral aberration drawings of the zoom lens of theexemplary embodiment 3 at the wide angle end and at the telephoto end,respectively, for the base period.

FIGS. 9C and 6D are lateral aberration drawings of the zoom lens of theexemplary embodiment 3 at the wide angle end and at the telephoto end,respectively, for the image stabilization period when a deflectioninclination of 0.3° is corrected.

FIG. 10 is a lens sectional view of a zoom lens of an exemplaryembodiment 4 according to the present invention at the wide angle end,and FIGS. 11A and 11B are longitudinal aberration drawings of the zoomlens of the exemplary embodiment 4 at the wide angle end and at thetelephoto end, respectively.

FIGS. 12A and 12B are lateral aberration drawings of the zoom lens ofthe exemplary embodiment 4 at the wide angle end and at the telephotoend, respectively, for the base period.

FIGS. 12C and 12D are lateral aberration drawings of the zoom lens ofthe exemplary embodiment 4 at the wide angle end and at the telephotoend, respectively, for the image stabilization period when a deflectioninclination of 0.3° is corrected.

FIG. 13 is a lens sectional view of a zoom lens of an exemplaryembodiment 5 according to the present invention at the wide angle end,and FIGS. 14A and 14B are longitudinal aberration drawings of the zoomlens of the exemplary embodiment 5 at the wide angle end and at thetelephoto end, respectively.

FIGS. 15A and 15B are lateral aberration drawings of the zoom lens ofthe exemplary embodiment 5 at the wide angle end and at the telephotoend, respectively, for the base period.

FIGS. 15C and 15D are lateral aberration drawings of the zoom lens ofthe exemplary embodiment 5 at the wide angle end and at the telephotoend, respectively, for the image stabilization period when a deflectioninclination of 0.3° is corrected.

FIG. 16 is a schematic view of part of a digital camera (image-pickupapparatus) according to the present invention.

The zoom lens of each of the exemplary embodiments is a taking lenssystem for use in the image-pickup apparatus.

In the lens sectional views shown in FIGS. 1, 4, 7, 10, and 13, the leftis the object side (expansion side) and the right is an image side(contraction side).

A first lens group L1 a-e has negative refractive power (opticalpower=inverse number of focal length); a second lens group L2 a-e haspositive refractive power; a third lens group L3 a-e has negativerefractive power; and a fourth lens group L4 a-e has positive refractivepower.

A second A lens component L2A1-5 with positive refractive powerconstitutes the second lens group L2 a-e. A second B lens componentL2B1-5 with positive refractive power constitutes the second lens groupL2 a-e.

The lens component means a lens system composed of a single and aplurality of lenses. An aperture stop SP is located adjacent to theimage of the second lens group L2 a-e for adjusting a light amount.

An image plane IP corresponds to an image-pickup surface of a solidstate image device (photoelectric transducer), such as a CCD sensor anda CMOS sensor, when used for a photographic optical system of a videocamera and a digital still camera, and it corresponds to a film surfacewhen used for a silver film camera.

In the aberration drawings, reference characters d, g, and F denote ad-ray, a g-ray, and an F-ray, respectively; characters ΔM and ΔS denotea meridional image plane of the d-ray and a sagittal image plane of thed-ray, respectively; the transverse chromatic aberration is representedby the g-ray; character Fno denotes a F number; and character Y denotesan image height. The Z-axis in the spherical aberration's graph isentrance pupil radius, the Z-axis in the astigmatism's, distortion's andchromatic aberration of magnification's graphs is image height.

In the following exemplary embodiments, the wide angle end and thetelephoto end are designated by both-end zooming positions in themechanically movable range along the optical axis of a lens group withvariable power (second, third, and fourth lens groups L2 a-e, L3 a-e,and L4 a-e in respective examples).

In each exemplary embodiment, during zooming from the wide angle end tothe telephoto end, each lens group moves in arrow direction in the lenssectional views.

In each exemplary embodiment, each lens group moves so that the spacebetween the first lens group Lla-e and the second lens group L2 a-e issmaller, the space between the second lens group L2 a-e and the thirdlens group L3 a-e is larger, and the space between the third lens groupL3 a-e and the fourth lens group L4 a-e is smaller at the telephoto endthan those at the wide angle end.

Specifically, during the zooming from the wide angle end to thetelephoto end, the first lens group L1 a-e moves (A1-A5) along part of atrajectory being convex toward the image.

Any of the second to fourth lens groups L2 a-e to L4 a-e moves (B1-B5;C1-C5; and D1-D5) toward the object.

The second lens group L2 a-e and the fourth lens group L4 a-e can bemoved (B1-B5; and D1-D5) independently or integrally for simplifying themechanism.

The aperture stop SP moves together with the second lens group L2 a-eduring the zooming.

The focusing can be performed by moving the first lens group L1 a-e.

In each exemplary embodiment, during zooming from the wide angle end tothe telephoto end, the fourth lens group L4 a-e located closest to theimage can be moved (D1-D5) toward the object.

Hence, in each exemplary embodiment, the back focus at the wide angleend is shortest.

Then, the refractive power is arranged so that the principal pointadjacent to the image is located closer to the image so as to increasethe back focus at the wide-angle end zooming position.

That is, the entire lens system is constructed to become more like aretrofocus type at the wide-angle end zooming position. Specifically, inorder to arrange lens groups to have the negative and positiverefractive power from the object to the image in that order, at thewide-angle end zooming position, the second to fourth lens groups L2 a-eto L4 a-e having positive resultant refractive power are arranged apartfrom the first lens group Lla-e with negative refractive power.

In the resultant refractive power of the second to fourth lens groups L2a-e to L4 a-e, the third lens group L3 a-e with negative refractivepower is also arranged closer to the image so that the principal pointadjacent to the image is located closer to the image so as tosufficiently increase the back focus in the entire system.

On the other hand, at the telephoto end zooming position, in order toreduce the full length of the entire lens system, the lens groups can bearranged to have the positive and negative refractive power from theobject to the image in that order so that the entire lens system isconstructed to become more like a telephoto type and the principal pointadjacent to the image is located closer to the object.

Specifically, at the telephoto end zooming position, the first lensgroup Lla-e with negative refractive power is moved (A1-A5) closer tothe second lens group L2 a-e with positive refractive power for forminga lens group having resultant positive refractive power.

Also, the third lens group L3 a-e is moved (C1-C5) closer to the fourthlens group L4 a-e for forming a lens group having resultant negativerefractive power. Thereby, the full length of the entire lens system isreduced at the telephoto end by forming the telephoto type.

The second lens group L2 a-e is composed of the second A lens componentL2A1-5 constituted by only a positive single lenses, and the second Blens component L2B1-5 having a negative lens and a positive lens. Thevibration is compensated by displacing the images formed by the zoomlens in a direction substantially perpendicular to the optical axis andmoving (displacing) the second A lens component L2A so as to have acomponent perpendicular to the optical axis. By constructing the secondA lens component L2A1-5 with one single lens, the weight of the zoomlens is reduced, and the image stabilization mechanism and the lensframe configured to hold the second A lens component L2A1-5 are reducedin size.

In particular, the load to a camera shake drive system for correctingblur is reduced, thereby miniaturizing the camera shake drive system andimproving the response to the decentering.

However, when the vibration is compensated with one single lens, it canbe necessary that the refractive power of the image stabilizing lens(the second A lens component L2A1-5) be suitably established and thesecond B lens component L2B1-5 be suitably constituted of lenses. Formaintaining the optical performances during compensating the vibration,the refractive power of the single lens may be rather weak; however, theimage stabilizing sensitivity can be reduced by doing so. As a result,the displacement during the image stabilization is unfavorablyincreased. Then, as will be described later, the refractive power of thesecond A lens component L2A1-5 is suitably established by satisfying aconditional equation (1).

For correcting chromatic aberration over the entire zooming range, thesecond lens group L2 a-e can be corrected in chromatic aberration tosome extent. Thus, the second B lens component L2B1-5 can be constructedso as to have at least one negative lens and one positive lens so as tosuppress the change in chromatic aberration during the zooming.

In each exemplary embodiment, the zoom lens includes the first lensgroup L1 a-e with negative refractive power, the second lens group L2a-e with positive refractive power, the aperture stop SP, and trailinglens groups arranged from the object to the image in that order. Then,by changing the space between the first lens group Lla-e and the secondlens group L2 a-e, the zooming is performed. The above is fundamentalconstruction of the zoom lens according to at least one exemplaryembodiment of the present invention.

At this time, a conditional equation (2) can be satisfied in addition tothe conditional equation (1). By satisfying the conditional equation(2), the distance between the mechanism of the aperture stop SP and thecamera shake drive system can be maintained to some extent, so that theycan be efficiently arranged without physical intervention, facilitatingthe entire system to be miniaturized.

During the zooming, the image stabilizing mechanism including the secondA lens component L2A1-5 is moved (B1-B5) integrally with the second lensgroup L2 a-e. The aperture stop mechanism is also moved integrally withthe second lens group L2 a-e so as to simplify the mechanism.

In each exemplary embodiment, the second A lens component L2A1-5, whichconstitutes part of the zoom lens, and has comparatively small size andweight and suitably established refractive power, is moved so as to havea component substantially perpendicular to the optical axis, so that theimage blur when the zoom lens is vibrated (tilted) is corrected.Thereby, the image blur is effectively corrected while the entireapparatus is miniaturized and simplified in mechanism, and the load ofthe driving means is reduced.

In each exemplary embodiment, by constructing the second A lenscomponent L2A1-5 for displacing an imaging position (images) in such amanner, excellent image stabilizing sensitivity is ensured.

In each exemplary embodiment, at least one of following equations issatisfied so as to have an effect corresponding to the equation.0.2<f2/f2A<0.6  (1)0.4<LP/fw<1.0  (2)0.05<d2A/fw<0.2  (3)55<V2A<85  (4)0.4<(Vp−Vn)/V2A<0.7  (5)2.4<ft/fw<4.0  (6)0.30<fw/bfw<0.70  (7)0.15<d23w/fw<0.40  (8)1.5<fw/f4<2.6  (9),where f2A and f2 are focal lengths of the second A lens component L2A1-5and the second lens group L2 a-e, respectively; LP is the distancebetween the lens surface closest to the image of the second A lenscomponent L2A1-5 and the aperture stop SP along the optical axis; fw andft are focal lengths of the entire system at the wide angle end and atthe telephoto end, respectively; d2A is the length of the positive lensof the second A lens component L2A1-5 in the optical axial direction;V2A is the Abbe number of the positive lens material of the second Alens component L2A1-5; Vn and Vp are the Abbe numbers of the materialsof the negative lens and the positive lens of the second B lenscomponent L2B1-5; bfw is the back focus at the wide angle end; d23w isthe axial air space at the wide angle end between the second lens groupL2 a-e and the third lens group L3 a-e; and f4 is the focal length ofthe fourth lens group L4 a-e.

Then, the technical meaning of each conditional equation will bedescribed.

The conditional equation (1) relates to the refractive power ratiobetween the second A lens component L2A1-5 and the second lens group L2a-e, and it is especially for balancing the optical performance and theimage stabilizing sensitivity during compensating vibration.

When the refractive power of the second A lens component L2A1-5 isreduced less than the lower limit of the conditional equation (1), theimage stabilizing sensitivity is lowered. Consequently, the displacementof the second A lens component L2A1-5 during compensating vibration isexcessively increased, so that the drive control of the second A lenscomponent L2A1-5 becomes difficult, unfavorably increasing the imagestabilizing drive system in size.

When the refractive power of the second A lens component L2A1-5 isexcessively increased over the upper limit, since the second A lenscomponent L2A1-5 is composed of only one positive lens, correction ofthe coma and transverse chromatic aberration during compensatingvibration is difficult.

The conditional equation (2) relates to the ratio between the distancebetween the lens surface closest to the image of the second A lenscomponent L2A1-5 and the aperture stop SP along the optical axis and thefocal length of the entire system at the wide angle end. The conditionalequation (2) is principally for miniaturizing the system by optimizingthe arrangement of the second A lens component L2A1-5 and the mechanismof the aperture stop SP.

When the ratio is reduced less than the lower limit of the conditionalequation (2), the second A lens component L2A1-5 excessively approachesthe mechanism of the aperture stop SP, so that they can unfavorablyintervene physically with each other.

When the ratio is excessively increased over the upper limit of theconditional equation (2), the second A lens component L2A1-5 can beexcessively separated from the mechanism of the aperture stop SP, sothat the system can be difficult to be miniaturized by effectively usingthe space.

The conditional equation (3) relates to the ratio between the wallthickness (center thickness) of the second A lens component L2A1-5composed of one positive lens, and the focal length of the entire systemat the wide angle end, and it can be used for obtaining the reduction inweight and high optical performances of the second A lens componentL2A1-5.

When the ratio is reduced less than the lower limit of the conditionalequation (3), the thickness of the positive single lens is excessivelyreduced, so that the lens can be difficult to fabricate and to establishthe optimum lens shape for correcting the spherical aberration.

When the ratio is excessively increased over the upper limit of theconditional equation (3), the thickness of the positive single lens isexcessively increased, unfavorably increasing the lens in weight andfull length at the wide angle end.

The conditional equation (4) defines the Abbe number of the positivesingle lens material of the second A lens component L2A1-5, and inparticular it can be used for correcting axial chromatic aberration atthe wide angle end during compensating vibration while suppressing thechanges in transverse chromatic aberration during zooming when thevibration is not compensated.

Since the second A lens component L2A1-5 is composed of a singlepositive lens for image stabilization, the transverse chromaticaberration tends to be generated during compensating vibration, so thatthe material can be suitably selected. When the Abbe number is reducedless than the lower limit of the conditional equation (4), thetransverse chromatic aberration is unfavorably deteriorated duringcompensating vibration. When the Abbe number is increased over the upperlimit of the conditional equation (4), the axial chromatic aberration isinsufficiently corrected especially at the wide angle end, unfavorablyincreasing the axial chromatic aberration to the over side.

The conditional equation (5) defines the Abbe number relationshipbetween the positive single lens material of the second A lens componentL2A1-5 and the materials of negative/positive lenses of the second Blens component L2B1-5, and it can be used for favorably correcting theaxial chromatic aberration.

It is generally useful that the aberration be corrected to some extentin each lens group itself of the zoom lens.

In each exemplary embodiment, since the second A lens component L2A1-5is composed of a single positive lens, the chromatic aberration iscorrected with the second B lens component L2B1-5 while being correctedwith the entire second lens group L2 a-e. When the relationship isreduced less than the lower limit of the conditional equation (5), theaxial chromatic aberration is insufficiently corrected especially at thetelephoto end, unfavorably increasing the axial chromatic aberration tothe under side. When the relationship is increased over the upper limitof the conditional equation (5), the axial chromatic aberration isinsufficiently corrected especially at the wide angle end, unfavorablyincreasing the axial chromatic aberration to the over side.

The conditional equation (6) relates to the focal length ratio betweenthe entire system at the wide angle end and the entire system at thetelephoto end. When the ratio is reduced less than the lower limit ofthe conditional equation (6), the sufficient zooming ratio may not beobtained. When the ratio is increased over the upper limit of theconditional equation (6), the zooming ratio is excessively increased,unfavorably increasing the entire length of the lens.

The conditional equation (7) relates to the focal length ratio betweenthe back focus at the wide angle end and the entire system at the wideangle end. This establishes an optimum condition for an image-pickupapparatus requiring a long back focus, such as a single lens reflexcamera. The back focus herein signifies the distance between theparaxial image plane and the lens surface adjacent to the image of thelens located closest to the image among lenses (optical elements) havinga curvature (power).

When the ratio is reduced less than the lower limit of the conditionalequation (7), the back focus at the wide angle end is excessivelyincreased, thereby increasing the lens full length at the wide angleend. The lens becomes more like a retrofocus type excessively, so thatthe distortion especially at the wide angle end is difficult to correct.

When the ratio is increased over the upper limit of the conditionalequation (7), the back focus is excessively reduced, so that the lenstends to intervene with a mirror and the exit pupil unfavorably comesclose to the image plane.

The conditional equation (8) defines the axial air space at the wideangle end between the lens surface closest to the image of the secondlens group L2 a-e and the lens surface closest to the object of thethird lens group L3 a-e. When the space is reduced less than the lowerlimit of the conditional equation (8), the second A lens componentL2A1-5 is located rather adjacent to the image plane, so that the imagestabilizing mechanism is difficult to arrange. When the space isincreased over the upper limit of the conditional equation (8), therefractive power of retrofocus type becomes weak especially at wideangle end, so that the back focus is difficult to be elongated.

The conditional equation (9) relates to the focal length ratio betweenthe fourth lens group L4 a-e and the entire system at the wide angleend, and it can be used for ensuring high optical performances and thelong back focus at the wide angle end. When the ratio is reduced lessthan the lower limit of the conditional equation (9), the refractivepower of the fourth lens group L4 a-e is excessively weaken, so that theback focus is unfavorably reduced especially at the wide angle end. Whenthe ratio is increased over the upper limit of the conditional equation(9), the refractive power of the fourth lens group L4 a-e is excessivelyincreased, so that the curvature of field is difficult to correctespecially at the wide angle end.

Additionally, the numerical ranges of the conditional equations (1) to(9) are set as follows:0.25<f2/f2A<0.38  (1a)0.45<LP/fw<0.7  (2a)0.07<d2A/fw<0.15  (3a)55<V2A<75  (4a)0.5<(Vp−Vn)/V2A<0.65  (5a)2.5<ft/fw<3.5  (6a)0.40<fw/bfw<0.60  (7a)0.20<d23w/fw<0.30  (8a)2.0<fw/f4<2.4  (9a).

In each exemplary embodiment, by such a structure described above, azoom lens having a zooming ratio of about 2.5 or more and a back focuslonger than its focal length can be obtained. Furthermore, by moving acomparatively small and light weight single lens so as to have acomponent substantially perpendicular to the optical axis, the imageblur when the zoom lens is vibrated (tilted) is corrected. Thereby, azoom lens is obtained which is capable of effectively correcting theimage blur while the entire apparatus is miniaturized and simplified inmechanism and the load of the driving means is reduced.

Numerical examples 1 to 5 respectively corresponding to the exemplaryembodiments 1 to 5 will be shown below. In each numerical example,reference character i denotes a face order from the object side;character Ri a radius of curvature of each face; character Di a memberwall thickness or an air space between the i^(th) face and the(i+1)^(th) face; and characters Ni and νi denote a refractive index andan Abbe number of the d-ray, respectively. Also, “e^(−X)” signifies“×10^(−X)” Character f denotes a focal length; character Fno an Fnumber; and character ω a half angle of view. The aspheric shape isexpressed by Numerical Formula 1: $\begin{matrix}{X = {\frac{\left( {1/R} \right)H^{2}}{1 + \sqrt{1 - \left( {H/R} \right)^{2}}} + {AH}^{2} + {BH}^{4} + {CH}^{6} + {DH}^{8} + {EH}^{10} + {FH}^{12}}} & {{Numerical}\quad{Formula}\quad 1}\end{matrix}$where X is the displacement in the optical axial direction from thesurface apex as a reference at the height h from the optical axis; R isthe paraxial radius of curvature; and A, B, C, D, E, and F are asphericfactors.

The relationship between the conditional equations described above andnumerals of the numerical examples will be shown in Table 1.

NUMERICAL EXAMPLES 1

f=17.50˜53.00 Fno=3.59˜5.86 2 =75.8°˜28.8°

R 1=74.641 D 1=4.50 N 1=1.516330 ν 1=64.1

R 2=−3856.041 D 2=0.15

R 3=98.417 D 3=1.60 N 2=1.622992 ν 2=58.2

R 4=14.489 D 4=8.52

R 5=−127.608 D 5=1.20 N 3=1.622992 ν 3=58.2

R 6=27.528 D 6=0.15

R 7=21.526 D 7=3.40 N 4=1.846660 ν 4=23.8

R 8=42.071 D 8=VARIABLE

R 9=−531.961 D 9=1.70 N 5=1.518229 ν 5=58.9

R10=−36.156 D10=4.53

R11=16.829 D11=0.80 N 6=1.846660 ν 6=23.9

R12=12.056 D12=4.20 N 7=1.487490 ν 7=70.2

R13=−71.553 D13=1.00

R14=APERTURE STOP D14=VARIABLE

R15=−28.778 D15=0.75 N 8=1.647689 ν 8=33.8

R16=12.243 D16=2.40 N 9=1.761821 ν 9=26.5

R17=51.593 D17=VARIABLE

R18=−62.665 D18=1.30 N10=1.491710 ν10=57.4

-   -   R19=−140.261 D19=−0.07        R20=1237.920 D20=2.69 N11=1.487490 ν11=70.2        R21=−17.585        \FOCAL LENGTH 17.50 31.07 53.00 VARIABLE SPACE\        D 8 33.74 13.03 3.04        R20=417.340 D20=3.80 N11=1.487490 ν11=70.2        R21=−18.474        \FOCAL LENGTH 18.69 32.08 53.27 VARIABLE SPACE\        D 8 33.62 13.53 3.23        D14 3.30 6.19 8.96        D17 7.34 4.45 1.68        ASPHERIC FACTOR        19 FACE : A=0.00000e+00 B=3.76648e−05 C=3.00374e−08        D=7.60709e−10 E=−8.99719e−12 F=0.00000e+00

NUMERICAL EXAMPLES 3

f=18.62˜53.32 Fno=3.63˜5.86 2ω=72.4°˜28.7°

R 1=70.299 D 1=3.40 N 1=1.516330 ν 1=64.1

R 2=601.574 D 2=0.15

R 3=85.189 D 3=1.60 N 2=1.622992 ν 2=58.2

R 4=14.573 D 4=8.08

R 5=−131.403 D 5=1.20 N 3=1.622992 ν 3=58.2

R 6=26.414 D 6=0.15

R 7=21.357 D 7=3.40 N 4=1.805181 ν 4=25.4

R 8=48.045 D 8=VARIABLE

D14 3.30 6.68 10.13

D17 8.24 4.86 1.41

NUMERICAL EXAMPLES 2

f=18.69˜53.27 Fno=3.63˜5.86 2ω=72.2°˜28.7°

R 1=80.198 D 1=3.40 N 1=1.516330 ν 1=64.1

R 2=1485.520 D 2=0.15

R 3=74.916 D 3=1.60 N 2=1.622992 ν 2=58.2

R 4=14.601 D 4=7.99

R 5=−141.698 D 5=1.20 N 3=1.622992 ν 3=58.2

R 6=25.795 D 6=0.15

R 7=21.179 D 7=3.40 N 4=1.805181 ν 4=25.4

R 8=46.880 D 8=VARIABLE

R 9=−302.692 D 9=1.90 N 5=1.487490 ν 5=70.2

R10=−34.091 D10=4.20

R11=16.673 D11=0.80 N 6=1.846660 ν 6=23.9

R12=12.277 D12=4.50 N 7=1.487490 ν 7=70.2

R13=−73.294 D13=1.00

R14=APERTURE STOP D14=VARIABLE

R15=−29.161 D15=0.75 N 8=1.639799 ν 8=34.5

R16=12.672 D16=2.60 N 9=1.784723 ν 9=25.7

R17=43.512 D17=VARIABLE

R18=−96.235 D18=1.50 N10=1.583060 ν10=30.2

-   -   R19=−437.245 D19=0.03        R 9=−212.350 D 9=1.90 N 5=1.516330 ν 5=64.1        R10=−33.748 D10=4.20        R11=16.638 D11=0.80 N 6=1.846660 ν 6=23.9        R12=12.089 D12=4.50 N 7=1.487490 ν 7=70.2        R13=−67.351 D13=1.00        R14=APERTURE STOP D14=VARIABLE        R15=−27.965 D15=0.75 N 8=1.639799 ν 8=34.5        R16=12.432 D16=2.60 N 9=1.784723 ν 9=25.7        R17=43.001 D17=VARIABLE        R18=−97.655 D18=1.50 N10=1.583060 ν 10=30.2    -   R19=−332.527 D19=0.04        R20=1043.264 D20=3.76 N11=1.487490 V11=70.2        R21=−17.869        \FOCAL LENGTH 18.62 31.88 53.32 VARIABLE SPACE\        D 8 32.81 13.04 2.78        D14 3.30 6.07 8.95        D17 7.20 4.43 1.55        ASPHERIC FACTOR        19 FACE : A=0.00000e+00 B=3.81779e−05 C=2.00413e−08        D=6.78143e−10 E=−4.60818e−12 F=0.00000e+00        \FOCAL LENGTH 18.57 31.77 53.32 VARIABLE SPACE\        D 8 33.51 13.31 2.76        D14 3.30 6.13 9.21        D17 7.37 4.55 1.46        ASPHERIC FACTOR        19 FACE : A=0.00000e+00 B=3.81884e−05 C=4.42863e−08        D=7.05773e−10 E=−1.04850e−11 F=0.00000e+00

NUMERICAL EXAMPLES 5

f=17.50˜53.05 Fno=3.63˜5.86 2ω=75.8°˜28.8°

R 1=76.749 D 1=4.00 N 1=1.518229 ν 1=58.9

R 2=5373.923 D 2=0.15

R 3=102.763 D 3=1.60 N 2=1.622992 ν 2=58.2

R 4=14.773 D 4=8.44

R 5=−137.895 D 5=1.20 N 3=1.622992 ν 3=58.2

R 6=26.312 D 6=0.15

R 7=21.399 D 7=3.40 N 4=1.805181 ν 4=25.4

R 8=47.704 D 8=VARIABLE

R 9=−273.402 D 9=1.70 N 5=1.518229 ν 5=58.9

R10=−34.874 D10=4.30

R11=16.793 D11=0.80 N 6=1.846660 ν 6=23.9

NUMERICAL EXAMPLES 4

f=18.57˜53.32 Fno=3.63˜5.86 2ω=72.5°˜28.7°

R 1=75.404 D 1=3.40 N 1=1.516330 ν1=64.1

R 2=787.756 D 2=0.15

R 3=88.153 D 3=1.60 N 2=1.622992 ν 2=58.2

R 4=14.835 D 4=8.15

R 5=−142.888 D 5=1.20 N 3=1.622992 ν 3=58.2

R 6=26.536 D 6=0.15

R 7=21.495 D 7=3.40 N 4=1.805181 ν 4=25.4

R 8=47.829 D 8=VARIABLE

R 9=−248.450 D 9=1.90 N 5=1.518229 ν 5=58.9

R10=−35.027 D10=4.20

R11=16.774 D11=0.80 N 6=1.846660 ν 6=23.9

R12=12.152 D12=4.50 N 7=1.487490 ν 7=70.2

R13=−68.717 D13=1.00

R14=APERTURE STOP D14=VARIABLE

R15=−29.501 D15=0.75 N 8=1.647689 ν 8=33.8

R16=12.252 D16=2.60 N 9=1.784723 ν 9=25.7

R17=44.558 D17=VARIABLE

R18=−89.852 D18=1.50 N10=1.583060 ν10=30.2

-   -   R19=−276.592 D19=0.07        R20=2759.039 D20=4.08 N11=1.487490 ν11=70.2        R21=−17.975        R12=12.120 D12=4.20 N 7=1.487490 ν 7=70.2        R13=−70.015 D13=1.00        R14=APERTURE STOP D14=VARIABLE        R15=−28.422 D15=0.75 N 8=1.647689 ν 8=33.8        R16=12.486 D16=2.40 N 9=1.784723 ν 9=25.7        R17=44.493 D17=VARIABLE        R18=−96.742 D18=1.50 N10=1.583060 ν10=30.2    -   R19=−203.231 D19=0.07        R20=954.142 D20=3.98 N11=1.487490 ν11=70.2        R21=−17.650        \FOCAL LENGTH 17.50 30.77 53.05 VARIABLE SPACE\        D 8 33.80 12.73 2.21        D14 3.30 6.21 9.72        D17 7.52 4.60 1.09        ASPHERIC FACTOR        19 FACE : A=0.00000e+00 B=3.76441e−05 C=7.06633e−08

D=6.54003e−10 E=−2.14684e−11 F=0.00000e+00 TABLE 1 CONDITIONAL EXEMPLARYEMBODIMENT EQUATION 1 2 3 4 5 (1)f2/f2A 0.34 0.32 0.33 0.33 0.33(2)Lp/fw 0.60 0.56 0.56 0.57 0.59 (3)d2A/fw 0.10 0.10 0.10 0.10 0.10(4)V2A 58.9 70.2 64.1 58.9 58.9 (5)(Vp − Vn)/V2A 0.62 0.59 0.60 0.590.60 (6)ft/fw 3.02 2.85 2.86 2.87 3.03 (7)fw/bfw 0.50 0.53 0.53 0.530.50 (8)d23w/fw 0.25 0.23 0.23 0.23 0.25 (9)fw/f4 2.36 2.30 2.24 2.302.25

Next, an exemplary embodiment of a single reflex camera using the zoomlens according to the present invention will be described with referenceto FIG. 16. Referring to FIG. 16, reference numeral 10 denotes a singlereflex camera body; numeral 11 an interchangeable lens having the zoomlens according to at least one exemplary embodiment of the presentinvention mounted thereon; numeral 12 a recording device configured torecord object images obtained through the interchangeable lens 11, suchas a film and an imager; numeral 13 a finder optical system configuredto facilitate observation of object images from the interchangeable lens11; numeral 14 a quick return mirror configured to rotate for switchingobject images from the interchangeable lens 11 to be transferred to therecording device 12 or to the finder optical system 13. When observingobject images through the finder, the object images focused on a focusplate 15 via the quick return mirror 14 can be observed by enlargingthem with an eyepiece optical system 17 after making them erect imageswith a penta prism 16. During shooting, the quick return mirror 14 isrotated in arrow direction, so that the object images are recorded bythe recording device 12. Reference numeral 18 denotes a sub mirror andnumeral 19 represents a focal point detector.

In such a manner, by incorporating the zoom lens according to at leastone exemplary embodiment of the present invention into an image-pickupdevice, such as a single lens reflex camera interchangeable lens, animage-pickup apparatus with high optical performances can be achieved.The present invention can also be applied to a single lens camerawithout a quick return mirror in the same way.

According to the exemplary embodiments described above, by moving partof lens groups constituting the zoom lens so as to have a componentperpendicular to the optical axis, image blur generated when the zoomlens is vibrated (tilted) is optically corrected so as to have correctedphotographic images. Thus, an image-pickup apparatus with stabilizedphotographic images, such as a photographic camera, a video camera, anelectronic still camera, and a digital camera, can be obtained.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the discussed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

This application claims the benefit of Japanese Application No.2005-263889 filed Sep. 12, 2005, which is hereby incorporated byreference herein in its entirety.

1. A zoom lens comprising: a first lens group with negative refractivepower; a second lens group with positive refractive power; a third lensgroup with negative refractive power; and a fourth lens group withpositive refractive power, which are arranged from an object side to animage side in that order, wherein each of the lens groups moves so thatthe space between the first lens group and the second lens group isreduced, the space between the second lens group and the third lensgroup is increased, and the space between the third lens group and thefourth lens group is reduced, at a telephoto end in comparison withspacing at a wide angle end, wherein the second lens group includes asecond A lens component composed of a single positive lens, and a secondB lens component composed of a negative lens and a positive lens withpositive refractive power as a whole, which are arranged from the objectside to the image side in that order, the second A lens componentdisplacing images in a direction substantially perpendicular to anoptical axis by having a component of it's displacement perpendicular tothe optical axis, and wherein the zoom lens satisfies the followingcondition:0.2<f2/f2A<0.6, where f2A and f2 are focal lengths of the second A lenscomponent and the second lens group, respectively.
 2. The zoom lensaccording to claim 1, wherein the zoom lens satisfies the followingcondition:0.05<d2A/fw<0.2, where d2A is the thickness of the positive lens of thesecond A lens component and fw is the focal length of the entire systemat the wide angle end.
 3. The zoom lens according to claim 1, whereinthe zoom lens satisfies the following condition:55<V2A <85, where V2A is the Abbe number of the positive lens materialof the second A lens component.
 4. The zoom lens according to claim 1,wherein the zoom lens satisfies the following condition:0.4<(Vp−Vn)/V2A<0.7, where V2A is the Abbe number of the positive lensmaterial of the second A lens component, and Vn and Vp are the Abbenumbers of the negative lens material and the positive lens material ofthe second B lens component, respectively.
 5. The zoom lens according toclaim 1, further comprising an aperture stop arranged adjacent to animage plane of the second lens group, wherein the aperture stop movesintegrally with the second lens group during zooming.
 6. The zoom lensaccording to claim 1, wherein the zoom lens satisfies the followingcondition:2.4<ft/fw <4.0, where fw and ft are the focal lengths of the entiresystem at the wide angle end and at the telephoto end, respectively. 7.The zoom lens according to claim 1, wherein the zoom lens satisfies thefollowing condition:0.30<fw/bfw<0.70, where bfw is the back focus at the wide angle end andfw is the focal length of the entire system at the wide angle end. 8.The zoom lens according to claim 1, wherein the zoom lens satisfies thefollowing condition:0.15<d23w/fw<0.40, where d23w is the axial air space between the secondlens group and the third lens group at the wide angle end and fw is thefocal length of the entire system at the wide angle end.
 9. The zoomlens according to claim 1, wherein the zoom lens satisfies the followingcondition:1.5<fw/f4<2.6, where f4 is the focal length of the fourth lens group andfw is the focal length of the entire system at the wide angle end. 10.The zoom lens according to claim 1, wherein images are formed on a solidstate image-pickup device.
 11. An image-pickup apparatus comprising; thezoom lens according to claim 1; and a solid state image-pickup devicefor receiving images thereon formed by the zoom lens.
 12. A zoom lenscomprising: a first lens group with negative refractive power; a secondlens group with positive refractive power; an aperture stop; and atleast one trailing lens group, which are arranged from an object side toan image side in that order, wherein the space between the first lensgroup and the second lens group is changed during zooming, and thesecond lens group includes a second A lens component composed of asingle positive lens, and a second B lens component composed of anegative lens and a positive lens with positive refractive power as awhole, which are arranged from the object side to the image side in thatorder, the second A lens component displacing images in a directionsubstantially perpendicular to an optical axis by having a component ofit's displacement perpendicular to the optical axis, and wherein thezoom lens satisfies the following conditions:0.2<f2/f2A<0.60.4<LP/fw <1.0, where f2A and f2 are the focal lengths of the second Alens component and the second lens group, respectively; LP is thedistance along the optical axis between the lens surface closest to theimage side of the second A lens component and the aperture stop; and fwis the focal length of the entire system at the wide angle end.
 13. Thezoom lens according to claim 12, wherein the zoom lens satisfies thefollowing condition:0.05<d2A/fw<0.2, where d2A is the thickness of the positive lens of thesecond A lens component and fw is the focal length of the entire systemat the wide angle end.
 14. The zoom lens according to claim 12, whereinthe zoom lens satisfies the following condition:55<V2A<85, where V2A is the Abbe number of the positive lens material ofthe second A lens component.
 15. The zoom lens according to claim 12,wherein the zoom lens satisfies the following condition:0.4<(Vp−Vn)/V2A<0.7, where V2A is the Abbe number of the positive lensmaterial of the second A lens component, and Vn and Vp are the Abbenumbers of the negative lens material and the positive lens material ofthe second B lens component, respectively.
 16. The zoom lens accordingto claim 12, wherein the aperture stop is arranged adjacent to an imageplane of the second lens group and moves integrally with the second lensgroup during zooming.
 17. The zoom lens according to claim 12, whereinthe zoom lens satisfies the following condition:2.4<ft/fw <4.0, where fw and ft are the focal lengths of the entiresystem at the wide angle end and at the telephoto end, respectively. 18.The zoom lens according to claim 12, wherein the zoom lens satisfies thefollowing condition:0.30<fw/bfw<0.70, where bfw is the back focus at the wide angle end andfw is the focal length of the entire system at the wide angle end. 19.The zoom lens according to claim 12, wherein the zoom lens satisfies thefollowing condition:1.5<fw/f4<2.6, where f4 is the focal length of the fourth lens group andfw is the focal length of the entire system at the wide angle end. 20.The zoom lens according to claim 12, wherein images are formed on asolid state image-pickup device.
 21. An image-pickup apparatuscomprising; the zoom lens according to claim 12; and a solid stateimage-pickup device for receiving images thereon formed by the zoomlens.
 22. A zoom lens according to claim 1, wherein the zoom lensadditionally satisfies the following conditions:0.4<LP/fw<1.0, wherein LP is the distance along the optical axis betweenthe lens surface closest to the image side of the second A lenscomponent and the aperture stop; and fw is the focal length of theentire system at the wide angle end.